Sorry I missed your question Im sure that in human hospitals they can find out with blood tests before any symptoms show, weve had people come in (complete with the dead snake) saying their pet had been bitten and there have been barely visible marks in some cases but no symptoms. The only thing weve done at the emergency clinic I worked at in these cases is a CBC. I cant find anything about this in any vet manuals and Ive asked other vets that say this is not a sign one way or the other but an older vet did CBC's on many snakebites or suspected snake bite victims and I have to say that his theory proved right every time, every dog that we tested, the ones that either already had symptoms or later developed them the CBC on the Vet Test machine that we used always gave us a 'bad reading' we got no counts at all, the ones that were tested that did not show any symptoms either at the time or later we would get a reading on everything, WBC, PCV, etc. That said there are other reasons why you can get a bad reading on a blood sample, anything from failure with the machine, another medical problem, a bad blood sample, blood not transferred correctly into the tubes. But for the amount of tests that we did while working with that particular vet at the very least it created some questioning for us (techs) and had another vet there looking into it. I dont know whats happened since last year as Im no longer there, neither is the older vet. Ive seen reports that say the effects from a snakebite can take as long as 24 hours to show and I only have the clients word to go with that as none of my dogs, have ever been bitten but if the clients are being honest, and I have no reason to doubt them it can take as little as an hour or so before the symptoms show as was the case with the Pit Bull I memtioned earlier. Chances are if its a baby snake its more likely to contain venom due to inexperience on their part. Some adults will hit with a dry strike as a warning when disturbed. Ive also heard reports (Loma Linda bite victims symptoms), that there is a question of whether the vipers and pit vipers are mutating somehow, a victim that caught the snake that bit him...he had symptoms from both types but only bitten by one.